Scientists speculate that there may have been a giant octopus in the Cretaceous ocean that was close in size to the mythical sea monster "Kraken". This extinct cephalopod, which may have been nearly 19 meters long, was one of the top predators in the ancient oceans.


Artist's impression of an extinct giant octopus, which may have been the size of a large marine reptile.

Image source: Masato Hattori/Science Photo Library

The researchers said the estimate was based on fossilized jawbones. Wear marks on its mandibles indicate that it preyed on animals with hard shells and bones.

This study, published in Science on April 23, overturns the long-held view that during the Cretaceous period from 143 million to 66 million years ago, giant marine reptiles such as mosasaurs and other vertebrates completely dominated the marine ecosystem. However, some scientists have suggested that conclusions about the octopus's maximum size, which is about the length of an articulated truck, and its role in the ecosystem should be cautious.

Study co-author Yasuhiro Iba, a paleontologist at Hokkaido University in Japan, said that this giant octopus was identified through chitinous jaw bones from the late Cretaceous period, but its size range, diet and role in the ecosystem have not been clearly determined until now.

To fill this research gap, Iba, Shin Ikegami, a paleontologist at Hokkaido University, and colleagues reanalyzed 15 giant octopus jaw bone fossils. At the same time, they used artificial intelligence to analyze carbonate rock layers and discovered 12 new giant octopus fossils.

The analysis divided these giant octopuses into two species: "Nanaimo octopus Jie's" and "Nanaimo octopus hardi". The study found that they are not only genetically related to the modern Dumbo octopus (genus Sooty octopus), but also belong to the same evolutionary branch as the modern big-eared octopus (species Griptaurus).

Based on the anatomy of modern octopuses, researchers estimate that the length of these giant octopuses' mantles, the main pouch-like part of their bodies, ranges from 67 centimeters to 443 centimeters. Including the tentacles, the body length of "Jie's Nanaimo octopus" is about 2.8 meters to 7.7 meters, while the body length of "Ha's Nanaimo octopus" can reach 6.6 meters to an astonishing 18.6 meters.

"Some people would question whether it could really grow to 19 meters, but I'm pretty sure about it," said Christian Klug, a paleontologist at the University of Zurich in Switzerland who was not involved in the study. Because mantle-to-tentacle length ratios vary widely among modern cephalopods, a lower or middle estimate of the species' size may be closer to reality.

The jawbones of these "sea monsters" showed severe signs of wear, including edge chips and scratches, with the largest specimen even losing about 10% of its jaw length. Researchers determined that these marks were caused by the hard bones of their prey being crushed. These prey range from crustaceans, bivalves, and even large fish.

Judging from the size and wear characteristics of the jawbones, they were once the top predators in the Cretaceous oceans, competing with large vertebrate predators such as Hoffmann's Mosasaurus, which could reach 17 meters in length. Iba said giant octopuses have evolved some characteristics similar to those of marine vertebrate predators, including powerful jaws and smooth bodies.

Neil Kelley, a paleontologist at Vanderbilt University in the United States, said that these fossil jaw bones clearly come from a large octopus, but the exact size is still uncertain. Modern octopuses feed on animals with hard shells, so extinct octopuses may have behaved the same way.

Kelley added that these "sea monster" octopuses are cold-blooded and can breathe underwater. Compared with mosasaurs and other top vertebrate predators that mostly move closer to the sea surface, they may be able to thrive deeper in the ocean and prey on different types of prey.

Related paper information: https://doi.org/10.1126/science.aea6285